Chromite ore processing residue is a by-product discharged during the production of dichromate. Chromite Ore Processing Residue contains water-soluble Cr6+ and is thus extremely toxic. If Chromite Ore Processing Residue is stacked in the open air without treatment, underground water sources, rivers or seas will be polluted to different degrees. As a result, the human health and the growth of plants and animals will be endangered seriously.
Generally, as the existing methods for detoxifying Chromite Ore Processing Residue (i.e., converting highly toxic Cr6+ into Cr3+), there are two categories, i.e., wet detoxification and dry detoxification. However, both the wet detoxification and the dry detoxification have their own problems. The wet detoxification is a method for reducing, in purpose of detoxification, Cr6+ in Chromite Ore Processing Residue in a liquid phase by adding a reductant. However, this method has high reagent consumption and high cost, and is still difficult to treat Chromite Ore Processing Residue on a large scale at present. In the dry detoxification, the purpose of detoxification is achieved by reducing Cr6+ in Chromite Ore Processing Residue into Cr3+ by strong reduction in a high-temperature reductive atmosphere. The conventional dry detoxification is to reduce toxic Cr6+ into nontoxic Cr6+ by heating it to about 1000° C. in a reductive atmosphere by using carbon as a reductant. This method has been widely applied to the treatment of Chromite Ore Processing Residue and has certain economic benefits. However, the method is accompanied with secondary dust pollution during the treatment, and has high investment cost and high energy consumption.
Plastic is a white pollutant. At present, there are various problems in the methods for treating plastics. Due to the presence of Cl in the plastics, it is likely to generate dioxin if the plastics are burnt. As a more practical method currently, the plastics are pyrolyzed to produce fuel oil and gas. Chinese Patent Application No. CN201110366027.9 disclosed a method for preparing fuel oil and gas from plastics in two steps, wherein, in the first step, HCl is volatilized at a low temperature, and in the second step, the plastics are pyrolyzed to produce oil and gas. Although this method is practical, the reaction period is long due to the implementation in two steps. In addition, during the implementation of the process, it is difficult to completely volatilize HCl, and part of the residual HCl easily enters the pyrolysis oil and gas in the second step so as to contaminate the pyrolysis oil and gas.
Additionally, a large amount of steel slag will be produced in China every year, and the liquid steel slag has a high temperature of about 1500° C. to 1700° C. The steel slag will become valuable resources if it is utilized fully. However, at present, there are few processes by which heat of steel slag can be effectively utilized.